Positive temperature control door lock system

ABSTRACT

An oven upper temperature safety control is provided in the instant invention by utilization of the door lock thermostat during the cooking modes of the oven to prevent the temperature of the oven reaching an unsafe level if failure of the temperature sensor control system occurs. The operation of the door lock thermostat as a temperature safety control is positively interrupted by actuation of the door locking system for the oven.

United States Patent [15] 3,639,727 Leach Feb. 1, 1972 [541 POSITIVE TEMPERATURE CONTROL 3,484,858 l2/l969 Jordan etal. ..-.2i9/4|3 DOOR LOCK SYSTEM [72] Inventor: James A. Leach, Shelby, Ohio [73] Assignee: Westinghouse Electric Corporation, Pittsburg'h, Pa.

[22] Filed: July 28, 1970 [2]] Appl. No.: 58,793

[52] US. Cl ..;.2l9/49l, 2l9/4l3 [5| 1 Int. Cl. ullfllh 37/00 [58] Field otSearch "ZN/412,413,491

[56] References Cited UNITED STATES PATENTS 3,549,862 l2/l970 Holtkamp et al. ..2l9/4l2 X Primary Examiner-Bernard A. Gilheany Assistant Examiner-F. E. Bell Attorney-F. H. Henson, E. C. Arenz and R. B. Farley [57] ABSTRACT An oven upper temperature safety control is provided in the instant invention by utilization of the door lock thermostat during the cooking modes of the oven to prevent the temperature of the oven reaching an unsafe level it failure of the temperature sensor control system occurs. The operation of the door lock thermostat as a temperature safety control is positively interrupted by actuation of the door locking system for the oven.

8 Claims, 2 Drawing Figures mcmm ran 1 1912 INVENTOR James A. Leach u -5 ATTORNEY POSITIVE TEMPERATURE CONTROL DOOR LOCK SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to ovens and, more particularly, relates to an oven upper temperature safety control system which provides a safety control for too high oven temperatures during the cooking modes of the oven.

2. Description of the Prior Art Oven control relays used in self-cleaning ovens are normally of an expanding wire thermal type and when these fail, they nonnally fail in a power-on position, if defective as installed or if the defect is developed during their operation. Failure of such a relay during a cooking operation of the oven, denies temperature control to the oven sensor permitting the oven to heat in an uncontrolled manner.

If such a failure occurred during a cooling operation, the oven temperature might well rise to a level well above the flash point of any residue present in the oven cavity. Under such circumstances, if the door to the oven was opened to thereby provide a readily reachable oxygen supply, a flash fire could result.

Furthermore, such an oven, when set in a cooking mode and having its relays fail (in a power on position), might well reach the saturation temperature of approximately l,280; and, at this temperature, even without an opening of the oven door, provide an outside temperature of the range surface which is at an unsafe level.

Accordingly, it would be desirable to provide a positive safeguard within any given oven system to prevent an unsafe temperature level while the oven is in a cooking mode, in the event that the oven control relays of the oven system failed in their power on position.

SUMMARY OF THE INVENTION An oven control system is provided in which a door lock thermostat is placed in series with one of the main power leads, so that excess temperatures within the oven cavity will cause the thermostat to operate to open the circuit and prevent additional power being supplied to the bake element. This thermostat is bypassed by the action of latching the oven door so that control of the oven in the clean phase is accomplished by a clean thermostat which sets a high temperature limit for the oven cavity in this mode. By this tandem thermostat arrangement, a positive control is provided for the temperature in the oven cavity whether the oven system is in the broil, bake or clean modes of operation. Desirably, in the cooking modes of operation when the door 'is not locked, the controlling thermostat opens between 560 and 600 F. to limit the top temperature to which the oven cavity may be subjected.

DRAWING DESCRIPTION For a better understanding of the invention, reference may be had to the preferred embodiment, exemplary of the invention, shown in the accompanying drawings, in which:

FIG. 1 is a schematic view of the oven system which embodies the instant invention; and

FIG. 2 is a table which identifies which contacts of the selector switch means are closed and in electrical contact for particular settings of the selector switch means.

PREFERRED EMBODIMENT OF THE INVENTION In FIG. 1, the control system for the oven of my invention is generally indicated by the numeral 10. An oven selector switch 12 may be set from an off position (shown in FIG. 1) to a position where a number of interrelated contacts within the selector switch may be placed in contacting or noncontacting position. The external terminals of the selector switch are identified by letter reference in FIG. I which correspond to the letter references across the top of the table of FIG. 2. FIG. 2 generally discloses the contacting elements which are engaged and provide a flow of current by the indication X" for each mode in which the oven may be placed.

A temperature controller 14 for the oven is illustrated in the bottom portion of FIG. I and is of the general bridge character and includes an auxiliary relay 16 which is normally controlled in accordance with operation of the temperature controller 14. The auxiliary relay switch means 16 is normally disposed in a leg of the temperature controlling means 14 and includes a pair of switches 18 and 20 which conventionally controlled in accordance with the operation of the temperature controller l4.

Since it is common practice in connection with heat cleaning ovens to provide means to ensure that the oven door is latched shut before a heat cleaning cycle is initiated and is in a condition to permit locking of the door as the temperature in the oven rises above the heat cleaning range a lock assembly is represented only by the dash line rectangle 22 and its control, in part, by the operation of a latch handle on the oven door is diagrammatically illustrated. Such a latching arrangement is of the same general character as disclosed in U.S. Pat. No. 3,387,874, owned by a common assignee, so that no further description of such a door locking arrangement is given in this application.

A source of electrical power for the oven and control system is provided by a conventional three-line source in which a nominal 240-volt alternating potential exists between the power connections denoted L1 and L2 and with I20 volts alternating potential between these hot lines and the neutral designated N.

Temperature controller 14 is of the general type described in Baker U.S. Pat. No. 2,962,575 and includes a hot wire which senses the temperature in the oven and actuates the switches 18 and 20 to close whenever the temperature sensed is below the temperature to which the temperature controller is set. Upon deenergization, the hot wire 24 cools and gradually permits these two switches to open. Delay in opening of the switches after relay deenergization gives time for a holding circuit to be established while the switch means is closed.

The temperature controller 14 is connected in a temperature controller circuit 26 which includes a secondary 28 of a transformer 30 during the normal cooking operations (i.e., bake, time bake, broil and auxiliary broil).

A temperature control bypass circuit 32 includes a pair of leads 34 and 36 which extend from the secondary 28 of the transformer 30 and the oven temperature controller l4, respectively, and are in electrical connection with a pair of contacts A and H formed in the selector switch 12. Since the terminals A and H are not in electrical carrying capacity during the aforementioned cooking operations, the oven temperature controller 14 is energized through the temperature controller circuit 26 that also includes a pair of leads 38 and 40, with the lead 38 being connected to the secondary 28 of the transformer 30 and the lead 40 being connected to the oven temperature controller 14. The temperature controller circuit 26 may normally be an I I-volt system, however, differing voltages may be used even though an ll-volt system was utilized and to carry out the invention.

An energizing circuit 42 for the transformer 30 includes a lead 44 which extends to and is an electrical connection with a contact of an ambient thermostat switch 46 that has its other contact connected through a lead 48 to neutral N. The ambient switch 46 is normally in a closed position unless the ambient temperature outwardly of the oven exceeds a certain value say, for example, Thus, a closed circuit network is provided between neutral and the primary winding 50 of the transformer 30. The opposite side of the energizing circuit 42 for the transformer 30 is completed by a lead 52 which extends to the terminal X on the selector switch 12. In the bake, latch, broil and auxiliary broil modes of operation, a circuit is completed to terminal L3 (FIG. 2) and from it to L2 voltage so as to energize the primary winding 50 of the transformer 30 and thereby energize the temperature controller 14.

During the clean operation of the oven, the transformer 30 is bypassed by a lead 54 which is electrically connected to the lead 52 on the L2 side of the primary winding 50, with this lead extending to a timer switch 56 which is actuated to an open condition by a timer motor 58 after a preset time of the oven in the clean mode. When the timer switch 56 is in closed position and the latch in latched position, a pair of solenoidoperated switches 60 and 62 are placed in one of their alternate positions indicated by dotted lines in FIG. I. In this position, (only attainable when the latch handle is in the latch position), switch 60 provides for a current flow from line L2 through a lead 64. Switch 62 in its dotted line position obtains its current from a lead 66 that extends to the L2 side of the supply. Since the contacts A and H are placed in a current carrying capacity in the clean mode, the oven temperature sensor 14 is bypassed by bypass circuit 32. This shorts out the internal switch of the temperature controller 14 which normally opens and closes in accordance with the differential between the sensed temperature of the temperature controller and the oven temperature. Thus, a low voltage (ll volts) is applied directly across the thermal delay element 24 so that the relay switches 18 and 20 are maintained in their closed current carrying condition.

Although the operation of the switches 60 and 62 has only been detailed electrically it should be clear that they are physically interrelated to the latching arrangement so that movement of this arrangement into locked condition causes the switches to move from their normally full line positions to the dotted position illustrated in FIG. 1. Such could be accomplished easily, for example, by placing these switches in a position where their switch blades would be physically contacted and moved by a solenoid plunger 63 of the operating latching arrangement.

The relay switch 20 is in circuit with a broil element 68 through a lead 70, with the opposite side of the broil element 68 attached to lead 72. Lead 72, in turn, is electrically connected to a lead 74 which extends through a pulse switch 76 that provides a pulsing current flow to the broil element. Since the contacts L3 and S are in a current carrying capacity during the clean mode of operation of the oven, current is provided across L1 to L2 through the broil element 68 to aid in cleaning of the oven. The pulsing of a switch 76 provides a cyclic energization of the broil element 68 to limit the total time in which the broil element 68 is energized.

A clean thermostat 78 is also disposed in the circuitry just described so as to limit the top temperature to which the interior of the oven is subjected. This thermostat is normally set at about 1,050 F. and thus ensures that all the combustibles that are burnable within the oven enclosure are fully consumed. At the upper temperature limit the thermostat 78, of course, opens so as to remove any electrical energization from the broil element 78. Interruption is accomplished because no circuit is then completed between line L2 and L1 and the fact that the switches 60 and 62 are in their dotted line positions has no effect in providing an energy source for the broil element 68. The relay switches I8 and 20, however, remain closed so that a reduction in temperature and a consequent reclosing of thermostat 78 again provides current to broil element 68. The cleaning cycle is permanently terminated by the opening of timer switch 56 which removes current from primary 50, thereby opening-relay switches 18 and 20. A clean cycle then may not be again initiated unless the selectorswitch and latching mechanism are moved through the latch and clean modes and after oven temperature has fallen below door lock temperature.

The bake cycle for the oven is initiated by current flow from line L2 through the relay switch 18 and from thence into a lead 80 which extends to and is in electrical connection with a bake element 82. Since the contacts B and L1 in the selector switch '12 are'in a current carrying condition in this mode of operation, LI is connected to the other side of the bake element 82 by means of a lead 84 extending to the L1 side through relay 20.

A control clock 86 is also provided to control a bake cycle of a set duration of time. This clock operates in a conventional manner and is connected across line L2 to neutral N, when a pair of contacts 88 and 90 within the clock are in engaged position. With these contacts closed, the primary 50 of the transfon'ner 30 is also provided with current so as to actuate the temperature controller 14. With the contacts 88 and 90 in a nonelectrical carrying capacity, (at the end of the time period set) the primary winding 50 also has no current maintained in it so that the temperature control sensor is disabled. With the primary coil 50 disabled and the temperature sensor 14 in an unenergized state, both the relay switches I8 and 20 move to open position so that no current is provided to the bake element 82 thereby terminating a time bake cycle.

In the auxiliary broil mode of operation (FIG. 2) the contacts L3 and T are in electrical carrying capacity, placing the broil element 68 across the lines LI and L2 and at the same time, the contacts L1 and M are in electrical current carrying capacity placing the auxiliary broil element 92 in an energized condition so that the elements 68 and 92 both contribute to the cooking of the food contained in the oven.

An oven pilot light 94 is also provided to indicate operation of the oven, with this pilot light in an energized condition for all modes of operation of the oven other than the latch and the off position. This pilot light is simply connected across neutral N and the supply line L2 through a lead 96 and the contacts P and L2, with the contact L2 having a lead 98 extending to neutral N.

Insofar as related, except for the solenoid-operated switches 60 and 62, the oven circuit 10 is substantially conventional and operates to provide fairly satisfactory temperature control operation. However, the switches 18 and 20 are subject to failure and normally would fail in an ON position so that the temperature sensor 14 would be unable to actuate these switches to open condition. In order to provide an upper temperature safety feature for the foregoing oven circuitry 10, a door lock thermostat 100 is placed in series with the supply line L2 and is connected to a lead 102 that extends to and is in contact with the switch 62 when it is in its full line position. By this arrangement, then, current flow from supply L2 may not pass inwardly into the oven system 10 unless the thermostat 100 is in a closed condition or unless the switch 62 is in latching position (clean mode). This thermostat is provided to open at a temperature of 560 to 600 F. For the bake, broil auxiliary broil and time bake modes of operation of the oven, then, the thermostat 100 provides a safety feature to prevent any of these modes from attaining a temperature which would tend to combust any flammable products within the oven. Of course, in the clean or latch mode of operation, of the oven system 10, the door lock thermostat I00 is bypassed and clean thermostat 78 provides, the upper temperature limit of l,050 F Since the switch 62 is in its dotted line position and lead 66 bypasses thermostat I00.

In review, it should be emphasized that the door lock thermostat 100, because of its position in the described circuitry, provide a safety temperature control for limiting the upper temperature of the oven I0 for all the cooking modes of it and that this thermostat is bypassed by the lead 66 and switch 62 only when the solenoid plunger 63 is actuated to the latch and then clean mode. With the oven 10 in the clean mode, the clean thermostat 78 still provides an upper temperature limit for the oven 10, but one which is significantly higher than that afforded to the oven 10 in the cooking modes. Further, when the oven 10 is in the clean mode of operation, door lock thermostat 100 still provides for positive locking of the latching arrangement 22 since opening of its contacts prevents removal of the solenoid plunger 63 from blocking interference with the unlatching functioning of the latching assembly 22.

It should be obvious from the foregoing description that an oven system has been provided which provides a safety feature not found in the prior art and that such is extremely important from a safety standpoint. Further although only a single embodiment of the invention has been described, it would be clear to one skilled in the art that many minor modifications could be made therein without departing from the spirit of the invention as disclosed in the foregoing specification.

I claim as my invention:

1. An oven system having cooking and cleaning cycles including:

a. a cooking actuating circuit including a pair of relays actuated by a temperature control means,

b. a clean actuating circuit including means for shorting out said temperature control means,

c. a door lock thermostat means disposed in series relationship in said cooking actuating circuit,

d. movable switch means for bypassing said door lock thermostat means when said oven system is in said cleaning cycle,

e. a latch arrangement for said oven system, and

f. said movable switch means being moved to bypass condition by said latch arrangement being moved to locked condition.

2. An oven system having cooking and cleaning cycles including:

a. a cooking actuating circuit including a pair of relays actuated by a temperature control means,

b. a clean actuating circuit including means for shorting out said temperature control means,

c. a door lock thermostat means disposed in series relationship in said cooking actuating circuit,

d. movable switch means for bypassing said door lock thermostat means when said oven system is in said cleaning cycle, and e. said movable switch means includes at least a pair of simultaneously actuated switches disposed in series relationship. 3. The combination set out in claim 2 wherein said oven system includes:

a. a three line supply, one of said lines being neutral and the other of said lines having a potential,

b. said door lock thermostat means being disposed between one of said lines having a potential and said cooking actuating circuit.

4. The combination set out in claim 3 wherein:

a. one of said switches is in series circuit relationship with a timer switch means.

5. The combination set out in claim 4 wherein:

a. the other of said switches is in series relationship with said one of said switches.

6. The combination set out in claim 5 wherein:

a. the other of said switches in one position being in a noncurrent carrying condition.

7. The combination set out in claim 6 wherein:

a. another thermostat means is provided for said oven system;

b. said thermostat means limits the top temperature of the oven system in the clean cycle.

8. The combination set out in claim 6 wherein:

a. said door lock thermostat means limits the upper temperature of the oven in the cooking cycle to a temperature below the flash point of any residue present in the oven cavity. 

1. An oven system having cooking and cleaning cycles including: a. a cooking actuating circuit including a pair of relays actuated by a temperature control means, b. a clean actuating circuit including means for shorting out said temperature control means, c. a door lock thermostat means disposed in series relationship in said cooking actuating circuit, d. movable switch means for bypassing said door lock thermostat means when said oven system is in said cleaning cycle, e. a latch arrangement for said oven system, and f. said movable switch means being moved to bypass condition by said latch arrangement being moved to locked condition.
 2. An oven system having cooking and cleaning cycles including: a. a cooking actuating circuit including a pair of relays actuated by a temperature control means, b. a clean actuating circuit including means for shorting out said temperature control means, c. a door lock thermostat means disposed in series relationship in said cooking actuating circuit, d. movable switch means for bypassing said door lock thermostat means when said oven system is in said cleaning cycle, and e. said movable switch means includes at least a pair of simultaneously actuated switches disposed in series relationship.
 3. The combination set out in claim 2 wherein said oven system includes: a. a three line supply, one of said lines being neutral and the other of said lines having a potential, b. said door lock thermostat means being disposed between one of said lines having a potential and said cooking actuating circuit.
 4. The combination set out in claim 3 wherein: a. one of said switches is in series circuit relationship with a timer switch means.
 5. The combination set out in claim 4 wherein: a. the other of said switches is in series relationship with said one of said switches.
 6. The combination set out in claim 5 wherein: a. the other of said switches in one position being in a noncurrent carrying condition.
 7. The combination set out in claim 6 wherein: a. another thermostat means is provided for said oven system; b. said thermostat means limits the top temperature of the oven system in the clean cycle.
 8. The combination set out in claim 6 wherein: a. said door lock thermostat means limits the upper temperature of the oven in the cooking cycle to a temperature below the flash point of any residue present in the oven cavity. 